Pearlescent pigments are commonly called pigments expressing pearlescent, iridescent, metallic shine. The pearlescent pigments are mainly manufactured by hydrothermal synthesis. However, recently, thin-film pigments are manufactured by sputtering or chemical vapor deposition (CVD) from foreign companies. The pearlescent pigments manufactured by the hydrothermal synthesis have disadvantages in that at the time of coating a metal and a metal oxide, gloss is not excellent since a refractive index is low, a surface is not flat, and a particle size distribution is not uniform. In addition, the thin-film pearlescent pigments manufactured by sputtering or CVD also have disadvantages in that productivity is reduced as compared to other processes.
A particle size, a shape, surface properties, refractive index, and the like, are important as characteristics of the pearlescent pigments. That is, since a large particle and a small particle have different ratio between a reflected light on a particle surface and a transmitted light transmitting particles, size of the particles needs to be uniform in order to obtain generally vivid colors. However, at the time of coating the metal or the metal oxide, it is difficult to form a uniform coating layer and an aspect ratio is decreased, and eventually, light reflectance is reduced, which deteriorates an interference effect. Therefore, it is required to have a particle size which is sufficiently uniform in implementing various pearl colors by light interference.
As the related art associated with the present invention, there is Korean Patent Publication No. 10-0853696 (Aug. 18, 2008), which discloses a method for manufacturing a plate alpha-alumina and a nano-metal coating pearlescent pigments with various colors and a large aspect ratio.